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Diffusion/Transcript
Transcript Text reads: The Mysteries of Life with Tim and Moby Tim and Moby are standing in a building. Tim is reading a piece of paper. Moby hands him a glass of water. MOBY: Beep. TIM: Hey, thanks. Tim takes the glass and drinks from it. TIM: Pwah! Tim spits out the water. TIM: It's salty! MOBY: Beep. Moby holds his hand over his mouth and laughs. TIM: Oh, that's real mature. Tim reads from a typed letter. TIM: Dear Tim and Moby, how come sugar sweetens a drink even when I don't stir it? From, Gene. Well, molecules do some moving on their own. An animation shows water molecules moving around rapidly. TIM: Molecules and energy naturally spread from areas of high concentration to areas of low concentration. This is called "diffusion". An animation shows a mass of liquid spreading into a widening circle. TIM: When you dump a spoonful of sugar into water, a little bit of it dissolves right away. But most of the crystals will settle to the bottom, where they slowly dissolve. An animation of a glass and some sugar illustrates what Tim describes. TIM: The water at the bottom of the glass will have higher concentrations of dissolved sugar than the water at the top of the glass. Text near the upper part of the glass reads: low sugar concentration. Text near the lower part of the glass reads: high sugar concentration. TIM: These differences in concentration are called gradients. An arrow points from the lower part of the glass with high sugar concentration toward the upper part of the glass with low sugar concentration. Text above the glass reads: concentration gradient. TIM: Molecules naturally move down concentration gradients. That is, from an area with a high concentration of molecules to an area of lower concentration. They keep doing this until a state of balance, or equilibrium, is reached. An animation illustrates the motion of molecules from a high-concentration area to a low-concentration area. The molecules spread out fairly evenly to reach equilibrium. MOBY: Beep. TIM: Well, no. Molecules don't actually stop moving at equilibrium, but their movement doesn't mix things up any more. See, molecules are in constant random motion; vibrating and bouncing against one another at all times. And that's what causes diffusion. The random movement of molecules gradually mixes stuff up. The more movement there is, the faster the rate of diffusion. Diffusion happens faster in gases than liquids, because the molecules in gases move more. An animation illustrates the process Tim describes. TIM: If you've ever smelled food cooking, or flowers from across the room, then you know what I mean. The molecules reach your nose pretty fast. An animation illustrates the aroma from a vaseful of roses spreading across a living room. TIM: Diffusion happens slowest of all in solids, where molecules vibrate but don't move around a whole lot. Three animations compare molecular movement in a gas, a liquid, and a solid. The molecules in the gas are the most sparse and most active, and the molecules in the solid are the most dense and least active. MOBY: Beep. TIM: Scientists are interested in diffusion because it touches so many different areas. It's responsible for the movement of nutrients and other substances across cell membranes. An animation shows nutrient molecules moving across a cell membrane. TIM: And it's used in a lot of different technologies, from water purification to nuclear power, but diffusion doesn't just apply to molecules. Images show a water purification plant and a nuclear power plant. An animation shows molecules moving. TIM: Energy, like heat and electricity, diffuses; too. Take this spoon, for example. Tim holds up an ordinary spoon. TIM: If Moby heats up one end of it, the high concentration of heat in that end will diffuse to the colder end. Moby shoots hot lasers from his eyes to the scoop end of the spoon. An arrow shows the heat moving from that end to the end that Tim is holding. TIM: Ow. Tim drops the spoon. TIM: Heat from the spoon will also diffuse into the surrounding air, a form of diffusion called thermal radiation. The spoon is now on the floor. Wavy lines indicate heat leaving the spoon and going into the air. TIM: Visible light is actually a type of thermal radiation. When something gets hot enough, some of its energy diffuses away in the form of visible light. Moby shoots his hot lasers at the spoon on the floor. The spoon changes color and glows. TIM: Anything that gives off light and heat, from the Sun to a candle to a lightbulb, is an example of diffusion at work. An animation shows the Sun, a lit candle, and a glowing lightbulb. TIM: Electricity works through diffusion, too. Electrons will move from the charged part of a wire to the uncharged part, creating an electric current. An animation shows a simple electrical circuit. Electrons in a wire travel from the positive side of a battery, through a lightbulb, and to the negative side of the battery. TIM: Hey, stay away from me. Ahhh. Moby is holding the spoon. He is putting an electrical charge into it and holding it toward Tim. Tim moves away from Moby. Moby follows, chasing Tim with the charged spoon. Category:BrainPOP Transcripts Category:BrainPOP Science Transcripts